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absolute magnitude absorption altitude angle angular diameter appear astronomical atmosphere attraction axis binary body bright celestial sphere centre Cepheid variables circle clusters comets components corresponding curve declination decrease density determined direction disc displacement Earth Earth's atmosphere eccentricity equal equator error galactic gravitation greater Greenwich horizon increase interval Jupiter known latitude length light lines longitude lunar Mars mass maximum mean distance measured Mercury meridian meteors method micrometer miles Milky Moon Moon's moving nebula node Observatory observed obtained occur orbit parallax parsecs perihelion period photographic planet Plate polar pole position proper motion radiation radius refraction relative revolution right ascension rotation satellites seen sidereal sidereal period solar eclipse solstice spectra spectral type spectroscopic spectroscopic binary spectrum stars stellar Sun-spot Sun's supposed surface synodic period telescope temperature theory transit Uranus variables variation velocity Venus vernal equinox visual magnitudes whilst zenith distance
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Page 242 - They have likewise discovered two lesser stars, or satellites, which revolve about Mars; whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost, five; the former revolves in the space of ten hours, and the latter in twenty-one and a half...
Page 73 - RULES TO KNOW WHEN THE MOVEABLE FEASTS AND HOLYDAYS BEGIN. EASTER DAY, on which the rest depend, is always the First Sunday after the Full Moon which happens upon, or next after the Twenty-first Day of March ; and if the Full Moon happens upon a Sunday, Easter Day is the Sunday after.
Page 29 - The amount of refraction when a ray of light passes from one medium into another varies with the angle of incidence, so that the sine of the angle of refraction bears a constant ratio to the sine of the angle of incidence. This ratio varies for each different medium, and is called the refracting power of the medium. The deviation of a ray in passing through a prism varies also...
Page 76 - A lunar month may be defined as the period from new Moon to new Moon, or from full Moon to full Moon, ie from conjunction to conjunction, or from opposition to opposition.
Page 329 - The radiation received from a plane surface varies as the cosine of the angle between the line of sight and the normal to the surface.
Page 91 - ... revolution around the sun. As to its rotation upon its axis, astronomers are not agreed. One opinion, rendered a century ago, was that a rotation on its axis was made in 24 hours, but recent observations have not confirmed it. A noted Italian astronomer says he has reason to believe that Mercury, like the moon, rotates on its axis in the same time that it makes a revolution about the sun. The synodic period of Mercury, or the time required from one conjunction to another, is 116 days. The greatest...
Page 242 - They have likewise discovered two lesser Stars, or Satellites, which revolve about Mars; whereof the innermost is distant from the Center of the primary Planet exactly three of his Diameters and the outermost five; the former revolves in the Space of ten Hours, and the latter in Twenty-one and a Half...
Page 164 - ... of a convex lens of crown glass, combined with a concave lens of flint glass, and therefor« producing an image without prismatic colours.
Page 130 - ... Secretary. A lesser man would have failed utterly to make any sort of headway amid the rocks and shoals with which the channels of War Office administration were now strewn, owing to the volcanic upheavals which had been taking place intermittently since 1854. These disturbances will be described in some detail in the next chapter. For the present it is sufficient to say that the root of the trouble was that, apart from the purely military side, there was a great number of different civil departments...
Page 206 - The squares of the periods of revolution of any two planets are proportional to the cubes of their mean distances from the sun.